Emphysema lung disease. Coloured 3D computed tomography (CT) scan of an axial sectioned view from below of the lungs of a patient with emphysema. Emphysema is a disorder where the air sacs in the lungs become enlarged and damaged reducing the surface area for the exchange of oxygen and carbon dioxide. The condition is causes impairment of respiratory function. The mosaic pattern represents the effects of airway obstruction. Pockets of air trapping (bullae) are represented in yellow. Relatively unaffected parts of lungs are represented in purple and blue.